Dispersion-based heat-sealable coating

ABSTRACT

Film-forming reactive systems for the surface-to-surface bonding and/or coating of substrates, more particularly for heat-sealable coatings are provided. The system is based on an aqueous dispersion of at least two epoxy-curable resins (I) and an epoxy compound as the curing component (II). The epoxy-curable resins are a polyurethane polymer containing epoxy-reactive functional groups present as the curable resin (Ia) and an aqueous dispersion of an acrylate and/or methacrylate homopolymer or copolymer containing carboxyl and/or methylol groups present as an additional curable resin (Ib). Also provided is a method for the production of laminates which employs the reactive system to bond substrates.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to two-component, film-forming reactive systemsfor the surface-to-surface bonding and/or coating of substrates, moreparticularly for heat-sealable coatings, based on aqueous dispersions of

at least one epoxy-curable resin (I) and

epoxy compounds as curing agent (II)

and to their use. The invention also relates to a process for theproduction of composites and adhesive-coated substrates.

2. Discussion of Related Art

The production of laminates and composites and especially the productionof base materials for flexible printed circuits requires specialadhesive systems. The requirements which such systems have to meet arevery stringent because on the one hand materials difficult to bond, suchas for example copper foils to polyimide films, have to be bonded andbecause, on the other hand, the composite materials obtained have to beflexible and highly resistant to heat. Solvent-containing adhesivesystems based on modified polyurethane, polyester, acrylate and epoxyresins are known to the expert for such purposes. Besides the basicproblems of solvents, systems of this type are often attended by thedisadvantage that the cure times are far too long, for example up to 14days in the case of polyurethane adhesive systems, or the curingtemperatures are too high, for example up to 240° C. in the case ofepoxy resin or acrylate systems. To eliminate the problems posed bysolvents, water-based systems have been developed. Thus, water-basedadhesives for flexible printed circuits containing dispersions ofacrylate (co)polymers and epoxy compounds are known from JP 87/153371and from JP 85/118781. A major disadvantage of systems such as these arethe relatively long cure times, for example 16 hours at 130° C. in thecase of JP 87/153371. JP 87/112676 describes water-containingpolyurethane adhesives based on polyurethane dispersions (A) obtainedfrom polytetramethylene glycol (MW 400 to 2,000), an organicdiisocyanate and a dimethylol carboxylic acid and also hydrazine ordihydrazides as chain extenders neutralized with tertiary amines and awater-soluble compound (B) containing two or more epoxy or aziridinerings per molecule. Although it is stated by way of example that variousfilms, for example PET and polypropylene, can be bonded to one anotherwith this adhesive, there is nothing in the document in question tosuggest to the expert that adhesives of the type in question could besuitable for heat-sealable coatings. In addition, there are noreferences to the production of non-blocking coatings or to the use ofthe adhesives for the production of flexible printed circuits.

The problem addressed by the present invention was to providewater-based reactive systems which would be capable of developing highbond strengths, even on substrates which are difficult to bond, such aspolyimides. In addition, high flexibility, high insulation resistance,high heat resistance and good solder bath resistance would all beguaranteed. The cure time would be relatively short while the curingtemperature would be below 200° C. In addition, the particularrequirement of blocking resistance would be satisfied. By this is meantthe non-tackiness of a film at typical ambient temperatures and storagetemperatures which is obtained by coating a substrate with the reactivesystem according to the invention and subsequent drying. In addition, anew raw material base and a different class of polymers would be openedup as starting material for systems of the type in question.

SUMMARY OF THE INVENTION

According to the invention, the problem stated above has been solved bytwo-component, film-forming reactive systems for the surface-to-surfacebonding and/or coating of substrates, more particularly forheat-sealable coatings, based on aqueous dispersions of at least oneepoxy-curable resin (I) and epoxy compounds as curing agent (II),characterized in that polyurethane polymers containing functional groupsreactive to epoxy compounds and, if desired, other resins are present asthe curable resin (Ia).

DETAILED DESCRIPTION OF THE INVENTION

Accordingly, the two-component reactive system according to theinvention contains dispersions of an epoxy-curable resin (I) anddispersed epoxy compounds as the curing agent (II). In contrast to thetwo Japanese applications cited above, the curable resin (Ia) present in(I) consists of polyurethane polymers containing functional groupsreactive to epoxy compounds. Amino groups, carboxyl groups and/orhydroxyl groups are particularly suitable as the reactive functionalgroups, carboxyl groups being preferred. Polyurethane polymers modifiedin this way are known to the expert.

Basically, there are a large number of starting materials which aresuitable for the production of polyurethanes. In approximate terms, theymay be divided into the so-called polyol component and the so-calledisocyanate component. Among the polyols, polyester polyols, polyetherpolyols and polyester polyether polyols are particularly important.Polyurethanes based on polyester polyols are preferred for the purposesof the invention. They are generally obtained by reaction of polyhydricalcohols with polybasic carboxylic acids. Suitable isocyanates for theproduction of polyurethanes are, for example, aliphatic, aromatic and/oralicyclic polyfunctional isocyanates. 4,4'-Diphenylmethane diisocyanate(MDI), isophorone diisocyanate (IPDI), tolylene diisocyanate (TDI) andtetramethyl xylene diisocyanate (TMXDI) are mentioned as examples.Further examples of the broad range of suitable polyol and isocyanatecomponents can be found in the relevant specialist and patent literatureon polyurethanes, for example in published European patent application354 471. The chain-extending step mentioned in that document is alsopossible. However, for the reasons of physiological compatibilitymentioned in the document in question, the chain-extending agents usedshould not be physiologically problematical such as, for example,hydrazine, diamino-diphenyl methane or the isomers of phenyldiamine andthe carbohydrazides or hydrazides of dicarboxylic acids.

The introduction of the epoxy-reactive functional groups into thepolymer chain is also known in principle to the expert. For example,hydroxyfunctional polyurethanes can be obtained by selecting a ratio ofOH groups to NCO groups of greater than 1 for the reaction of the polyoland isocyanate components. Carboxyl groups can be introduced, forexample, by adding one part of dihydroxy carboxylic acid to the polyolcomponent before it is reacted with the isocyanate component. Suitableamino-functional polyurethanes can be obtained, for example, by reactionof isocyanate-containing polyurethanes with polyfunctional aminocompounds providing the isocyanate group is present in less than theequivalent quantity. Further information on the introduction of suchfunctional groups, more particularly the carboxyl groups particularlypreferred for the purposes of the invention, can also be found in thepublished European patent application cited above.

Suitable polyurethane polymers may also contain different epoxy-reactivegroups. However, those in which the sum total of the acid value, OHvalue and amine value is on average 0.1 to 40 are also suitable.Polyurethane polymers in which the sum total mentioned is between 0.3and 20 are particularly suitable. A range of 0.5 to 5 is preferred.Basically, polyurethanes containing at least an average of twoepoxy-reactive functional groups are preferred for the purposes of theinvention. Among such polymers, those in which these reactive groups areterminally positioned are particularly suitable. So far as performanceproperties, particularly flexibility and bond strength, are concerned,polyurethanes with an average molecular weight of from about 7,000 to50,000 are preferably used. Particularly good results are obtained withpolyurethanes having an average molecular weight in the range from10,000 to 30,000. Both here and in the following, the average molecularweight is understood to be the weight average.

Suitable epoxy compounds are known to the expert both from the patentliterature and from encyclopedias. For example, the production,properties and use of epoxy compounds are described in detail inUllmann, Enzyklopadie der technischen Chemie, 4th Edition, Vol. 10,Verlag Chemie, Weinheim/Bergstrasse 1974, pages 563 et seq. Commerciallythe most important epoxy compounds include those based on bisphenol Aand/or novolak. Besides these, heterocyclic epoxy compounds are alsoparticularly suitable. According to the invention, epoxy resindispersions are used. In principle, any dispersible epoxy resins aresuitable. This applies both to the emulsifier-containing dispersions andto corresponding self-emulsifying systems. Such epoxy compounds astriglycidyl isocyanurate, polyethylene glycol diglycidyl ether orsorbitol polyglycidyl ether are also suitable. Instead of thedispersible epoxy resins, water-soluble epoxy compounds may also becompletely or partly used. The epoxy compounds suitable for use inaccordance with the invention preferably contain an average of at leasttwo epoxy groups. Epoxy compounds with an epoxy equivalent of 100 to4,000 are particularly preferred. An epoxy equivalent is understood tobe the quantity in grams present in 1 mole of epoxy compound.Particularly good results are obtained with epoxy compounds in whichthis value is between 150 and 600.

In one preferred embodiment of the invention, the dispersion of anepoxy-curable resin (I) contains acrylate and/or methacrylatehomopolymers or copolymers with carboxyl and/or methylol groups indispersed form as a further curable resin (Ib) in addition to thepolyurethanes (Ia) already described. (Meth)acrylate polymers modifiedin this way are known to the expert. Acrylic acid and methacrylic acidand also salts and esters thereof are mentioned as examples of suitable(meth)acrylates for the production of such polymers. The alcoholcomponent of these esters preferably contains 1 to 6 carbon atoms. Sofar as the polymer dispersions or emulsion used in accordance with theinvention are concerned, the expert may usefully resort to those whichhave been produced by emulsion polymerization. The monomers mentionedmay of course also be (co)polymerized with other ethylenicallyunsaturated monomers providing they are copolymerizable. Suitablemonomers such as these are any of those containing ethylenicallyunsaturated or vinyl groups.

The vinyl compounds include, for example, vinyl chloride and vinylesters, such as vinyl acetate, vinyl propionate, and even vinyl fattyacid esters, such as vinyl laurate, and also vinyl alcohol. Suitablestyrene compounds are styrene, halostyrenes, such as chlorostyrene,fluorostyrene and iodostyrene; alkyl styrenes, such as methyl styreneand 2,4-diethyl styrene, cyanostyrenes, hydroxystyrenes, nitrostyrenes,aminostyrenes and/or phenyl styrenes. Suitable derivatives of theacrylic compounds also include acrylonitrile for example. The carboxylgroups present in accordance with the invention in the polymersdescribed above may be introduced, for example, by using acrylic acidand/or methacrylic acid as monomers in the polymerization reaction.Methylol groups are obtained, for example, by the use of hydroxystyrenesor by copolymerization of vinyl acetate and subsequent saponification.

As already mentioned, it has long been known to the expert that monomersof the type in question can be added to form polymers in an aqueousmedium under emulsion polymerization conditions, as described forexample in Ullmann, loc. cit., Vol. 19, pages 11-21, pages 132 et seq.and pages 370-373 and in Encyclopedia of Polymer Science andEngineering, Volume 6, Wiley & Sons, New York, 1986, pages 1 to 51.Suitable monomers include, for example, vinyl compounds, the acrylatesalready mentioned and corresponding derivatives.

Polymers suitable for the purposes of the invention are, for example,(meth)acryl/styrene/acrylonitrile copolymers or polybutyl methacrylate.Homopolymers of acrylic acid and methacrylic acid are also suitable. Thepolymers mentioned above are particularly preferred when they have anaverage molecular weight of 50,000 to 300,000. Homopolymers andcopolymers in which the sum total of acid value and OH value is between1 and 40 are preferred for the purposes of the invention. Particularlygood results are obtained with the polymers mentioned when the sum totalin question is between 3 and 15, but more particularly between 4 and 10.

The ratio of the curable resins is of particular importance in regard toperformance results. According to the invention, the ratio by weight ofthe curable resin (Ia) to resin (Ib) is in the range from 100:0 to 5:95.As a general rule, it may be said that, the larger the polyurethanecomponent, the more flexible the film formed from the reactive systemwhereas, the higher the percentage of the other curable resin, thehigher the heat resistance value will be. Even a relatively smallpercentage of (Ib) leads to distinctly improved values in regard to thelast-mentioned property. Accordingly, the preferred range is between99:1 and 25:75. A particularly optimal and, hence, preferred ratio of(Ia) to (Ib) is 98:2 to 50:50. The ratios mentioned are based on thesolids content of the dispersion.

The ratio of curable resin (I) to curing agent (II) is also ofparticular importance. The ratios of the individual components to oneanother and the specification of these components do of course interactwith one another in influencing the performance properties of thereactive systems according to the invention or rather the films formedfrom them. Thus, reactive systems with a broad range of performanceproperties can be formulated via the ratio between the quantities ofindividual components, their molecular weights and theirfunctionalities. Thus, formulations with high initial tack andformulations which give a particularly blocking-resistant coating can beproduced. Accordingly, the ratio by weight of resin (I) to curing agent(II) can vary over a preferred range of 1:5 to 10:1. A range of 1:1 to5:1, in which optimal results are obtained, is particularly preferred.

To enable the curing process to be carried out in two stages, namely atroom temperature and at elevated temperature, and to promote theformation of a so-called interpenetrating network (IPN), the dispersionshould contain either 2 to 15% by weight, based on the solids content,of a polyaziridine or 2 to 30% by weight, based on the solids content,of a phenol/resol resin in addition to components (I) and (II) in apreferred embodiment of the invention.

The polyaziridine is a polyfunctional aziridine corresponding to thefollowing general formula: ##STR1## in which R is n organic aliphaticradical or a hydrogen atom,

X is an alkylene group which may contain an ester group, an ether group,an amide group or a similar inert group,

R' is an alkyl group containing 1 to 10 carbon atoms and

m is a number of 2 to 4.

It may be prepared in known manner by reaction of alkyl aziridines withcompounds containing NH-reactive groups. Preferred polyaziridines arethose in which R' is methyl, ethyl, propyl, butyl, ##STR2## where n=1 to3, l=1 to 3, and m is a number of 2 to 3 and R is a CH₃ --CH₂ --Cradical.

The addition of the polyaziridine results in:

an improvement in adhesion at lamination temperatures between roomtemperature and 90° C.,

accelerated curing at room temperature,

an improvement in heat resistance and resistance to chemicals wherecuring is carried out at room temperature.

The phenol/resol resin is also a known product and is obtained bycondensation of phenols, cresols and the like with formaldehyde. Liquidphenol resols are preferred. Their addition produces a furtherimprovement in the heat resistance of the adhesive film.

In one particular embodiment of the invention, the reactive systems mayalso contain typical additives in a total quantity of up to 30% byweight, based on the total solids content of the reactive system, inaddition to the dispersions of resin (I) and curing agent (II). Examplesof a few typical additives are given in the following. Catalysts suchas, for example, tertiary amines or phosphoric acid or derivativesthereof may be present, preferably in a quantity of up to 1% by weight.Coupling agents, such as silanes, titanates and zirconates, may bepresent in a quantity of up to 1% by weight. In order to keep thesurface open for a long period during film formation, high-boilingsolvents may be added in a quantity of up to 5% by weight. Foaminhibitors and wetting aids are typically present in quantities of up to2% by weight. Acid anhydrides or even styrene/maleic anhydride resins,for example, may be present as the crosslinking agent or wetting aid ina quantity of up to 10% by weight. A flexibilizer, for example NBRrubber with a molecular weight of 30,000 to 200,000, may be added in aquantity of up to 10% by weight for special applications. Polyesterswith an average molecular weight of around 600 to 15,000 or even glycolethers may be present as plasticizers in quantities of up to 5% byweight. Other possible additives are flameproofing agents,preservatives, etc. and effective quantities thereof are known to theexpert from the literature and need not be mentioned here. Thepercentages by weight mentioned above are again based on the totalsolids content of the reactive system which is preferably in the rangefrom 30% by weight to 75% by weight and more preferably in the rangefrom 40% by weight to 65% by weight.

Using the reactive systems according to the invention, it is possible toproduce adhesive-coated substrates which are suitable, for example, forthe production of flexible printed circuits. To this end, the reactivesystem is applied to the substrate, for example a metal foil, such ascopper foil, after thorough mixing of the dispersions of the resins (I)and the curing agent (II). This can be done by roller coating, spraycoating, spread coating, knife coating or dip coating. The reactivesystem is generally applied in a layer thickness of 15 to 40 μm andpreferably in a layer thickness of 20 to 25 μm. The substrate thuscoated is then dried at a temperature below the reactivationtemperature. Accordingly, the drying temperature should not exceed 120°C. to a significant extent, if at all. Drying may be carried out, forexample, in standard drying tunnels. Using a standard drying tunnel 4meters in length, the coating of films in accordance with the inventionmay be carried out at film speeds of 10 to 20 meters per minute, forexample at temperatures of 120° C. and with a throughput ofapproximately 4,000 m³ of air per hour. The adhesive-coated substrateobtained in this way is blocking-resistant, i.e. is not tacky at normalstorage temperatures and ambient temperatures.

Blocking-resistant systems such as these afford the advantage over theprior art that, for storage, the substrate does not have to be coveredby an additional protective film on its coated side. Films coated inaccordance with the invention may thus be stored in the form of rollsfree from protective films or cover films. Accordingly, there is noprotective film or cover film to be removed in the practical applicationof the coated substrates produced in accordance with the invention.Substrates thus coated in accordance with the invention may be used forthe production of laminates or composites. To this end, they aresubjected to hot pressing with another substrate. In other words, theadhesive-coated substrate is reactivated by heat and joinedsurface-to-surface to the other substrate by application of pressure,followed by curing. The pressure applied during the hot pressing step isdependent on the particular machine used and on the laminates orcomposites to be produced and is typically in the range from 5 to 200bar. Establishment of the optimal pressure for the particularcombination is within the scope of the expert's experience. Reactivationand curing preferably take place at temperatures in the range from 140°to 170° C. Another advantage of the invention lies in the short curetimes of 30 to 60 minutes.

The reactive systems according to the invention may of course also beused for the in-line production of laminates or composites. Thiseliminates the need for intermediate storage and, instead, thesubstrates are joined surface-to-surface (in-line) immediately aftercoating, optionally after brief preliminary drying of the reactivesystem applied, and the reactive system is subsequently cured.Accordingly, there is no need for intermediate storage of the coatedsubstrate (off-line process). Laminates or composites with more than twosubstrates which may consist of a variety of materials may of course beproduced both by the in-line process and by the off-line process. Forin-line lamination, the expert may select the ratio of resins (Ia) and(Ib) to one another and to the curing component--as alreadydescribed--in such a way that the reactive system according to theinvention has a slightly higher initial tack. Although this is often atthe expense of blocking resistance, blocking resistance is not animportant factor in the in-line process.

Accordingly, the reactive systems according to the invention areparticularly suitable for the production of multiply composites andlaminates. The substrates may be metal foils, plastic films, wovencloths, nonwovens, special papers and/or cardboard. Copper, aluminium,lead and constantan foils are mentioned as examples of metal foils.Particularly suitable plastic films are films based on polyethyleneterephthalate (PETP), polyimide (PI), polycarbonate (PC), polyesterether ketone (PEEK) and so-called liquid crystal polymers (LCP). Wovencloths of PETP or polyamide (PA), for example, are also suitablesubstrates. Nonwovens of PETP or polyaramide may also be used. Thespecial papers and cardboards are those based on polyaramide orpresspahn.

Copper foils coated in accordance with the invention applied under heatand pressure to other flexible substrates, such as Kapton® or polyesterfilm, as described above form composites which are suitable for theproduction of flexible printed circuits. The corresponding furtherprocessing of films provided with heat-sealable coatings is known as drylamination.

After thermal curing, the reactive systems according to the inventionform films which develop high mechanical, thermal and chemical stabilityin the laminates or composites mentioned. In addition to the productionof high-temperature-resistant, flexible printed circuits, the reactivesystems according to the invention may also be used for the productionof high-temperature-resistant insulating materials. In the presentcontext, insulating materials are understood above all to be cablesheaths, cover films for circuits and coil windings.

The invention is illustrated by the following Examples.

EXAMPLES Example 1

A water-based reactive system according to the invention contains indispersed form

5 parts by weight of a carboxyfunctional polyester urethane with anaverage molecular weight of around 25,000 and an acid value of 0.7±0.3

5 parts by weight of a methacryl/styrene/acrylonitrile copolymer with anaverage molecular weight of around 200,000 and an acid value of 5.5±0.5and

5 parts by weight of an epoxy resin based on bisphenol A with an epoxyequivalent weight of around 500.

After drying at around 120° C., the formulation mentioned above givesblocking-resistant films.

Example 2

A water-based reactive system according to the invention contains indispersed form:

31 parts by weight of a carboxyfunctional polyurethane with an averagemolecular weight of around 25,000 and an acid value of 0.7±0.3

8 parts by weight of a carboxyfunctional polyurethane with an averagemolecular weight of around 10,000 and an acid value of 0.7±0.3

1 part by weight of a methacryl/styrene/acrylonitrile copolymer with anaverage molecular weight of around 200,000 and an acid value of 5.5±0.5

5 parts by weight of an epoxy resin based on bisphenol A with an epoxyequivalent of around 500 and

5 parts by weight of an epoxy resin based on bisphenol A with an epoxyequivalent of 170.

After drying, this reactive system gives a coating with high initialtack and is particularly suitable for in-line lamination.

The quantities in Examples 1 and 2 are based on the particular solidscontent.

Example 3

A reactive system according to Example 1 was applied to a 35 μm thickcopper foil in a layer thickness of 20 to 25 μm. A 20 μm thick, compactnon-blocking adhesive film was obtained after drying at 120° C.

Example 4

The coated copper foil according to Example 3 was laminated with a 23 μmthick polyethylene terephthalate film at 140° C. In the adhesion test,material failure occurred. In the heat resistance test, neitherdelamination nor bubble formation was observed after 1 day at 155° C.After tempering for 30 minutes at 170° C., a solder bath resistance ofmore than 45 seconds at 230° C. was observed.

Example 5

The coated copper foil according to Example 3 was laminated with a 50 μmthick Kapton® film at 170° C. In the adhesion test, material failureoccurred. In the heat resistance test, no delamination or bubbleformation was observed after 1 day at 220° C. After heating for 30minutes at 170° C., a solder bath resistance of more than 60 seconds at288° C. was observed.

Example 6

A polyester film was coated with the reactive system according toExample 1, dried and then laminated with a polyaramide film at 140° C.The adhesion test resulted in material failure. In the heat resistancetest, there was no delamination or bubble formation after 1 day at 155°C.

Example 7

A polyester film was coated with the reactive system according toExample 1 and, after drying, was hot-pressed with a presspahn substrate.In this case, too, the adhesion test resulted in material failure. Inthe heat resistance test, no separation of the substrates nor any bubbleformation occurred after 1 day at 130° C.

Example 8

The positive effect of polyaziridine is illustrated by the followingExample:

A polyester film was coated with the reactive system according toExample 2, to which 5% of the polyaziridine CROSSLINKER CX-100 (aproduct of ICI), based on the solids content, had been added, dried andlaminated in-line with polyaramide paper at around 60° C. The adhesiontest resulted in material failure. In the heat resistance test, therewas no delamination or bubble formation after 48 h at 55° C.

Example 9

The positive effect of a phenol/resol resin is illustrated by thefollowing Example:

a) 2 Parts by weight of the polyurethane described in Example 1,

10 parts by weight of the acrylate copolymer described Example 1,

6 parts by weight of the epoxy resin described in Example 1

were mixed and the resulting mixture was applied to a copper foil anddried at 120° C.

b) 1 Part by weight of a liquid phenol resol resin was added to themixture described above, after which the mixture was likewise applied toa copper foil and dried at 120° C.

Both coatings were pressed for 1 h at 170° C. with 8 layers of aphenolic resin prepreg. Adhesive strengths of 4.2 to 4.5 N/3 mm weremeasured for sample a) and 4.6 to 4.9 N/3 mm for sample b). Sample a)had a solder bath resistance of 2 s at 260° C. while sample b) had asolder bath resistance of 22 s at 260° C.

We claim:
 1. A composition of matter useful as a film-forming reactive system for the surface-to-surface bonding and/or coating of substrates, said composition comprising an aqueous dispersion comprised of:a polyurethane polymer containing epoxy-reactive functional groups as a first curable resin, having a sum of an acid value, a hydroxyl value and an amine value of from 0.1 to 40, an acrylate and/or methacrylate homopolymer or copolymer containing carboxyl and/or methylol groups having a sum of an acid value and hydroxyl value from 1 to 40 is present in dispersed form as a second curable resin, an epoxy compound as a curing component for said first curable resin and said second curable resin.
 2. A composition as claimed in claim 1 wherein the ratio by weight of said first curable resin to said second curable resin is at least 5:95.
 3. A composition as claimed in claim 1 wherein the ratio by weight of said first curable resin to said second curable resin is in the range from 98:2 to 50:50.
 4. A composition as claimed in claim 1 wherein the ratio by weight of the sum of the weights of said first curable resin and said second curable resin to said epoxy compound is in the range from 1:5 to 10:1.
 5. A composition as claimed in claim 1 wherein the ratio by weight of the sum of the weights of said first curable resin and said second curable resin to said epoxy compound is in the range from 1:1 to 5:1.
 6. A composition as claimed in claim 1 wherein the epoxy-reactive functional groups of said polyurethane polymer are carboxyl and/or hydroxyl groups.
 7. A composition as claimed in claim 1 wherein the epoxy-reactive functional groups of said polyurethane polymer are carboxyl groups.
 8. A composition as claimed in claim 1 wherein said polyurethane polymer has a weight average molecular weight of 7,000 to 50,000.
 9. A composition as claimed in claim 1 wherein said polyurethane polymer has a weight average molecular weight of 10,000 to 30,000.
 10. A composition as claimed in claim 1 wherein said polyurethane polymer contains at least an average of two epoxy-reactive functional groups.
 11. A composition as claimed in claim 1 wherein the sum total of acid value, hydroxyl value and amine value of said polyurethane polymer is on average 0.3 and
 20. 12. A composition as claimed in claim 1 wherein the sum total of acid value, hydroxyl value and amine value of said polyurethane polymer is on average 0.5 to
 5. 13. A composition as claimed in claim 1 wherein said acrylate and/or methacrylate homopolymer and/or copolymer has a weight average molecular weight of 50,000 to 300,000.
 14. A composition as claimed in claim 1 wherein said acrylate and/or methacrylate homopolymer and/or copolymer has a sum total of acid value and OH value of 3 to
 15. 15. A composition as claimed in claim 1 wherein said acrylate and/or methacrylate homopolymer and/or copolymer has a sum total of acid value and OH value of 4 to
 10. 16. A composition as claimed in claim 1 wherein said epoxy compounds have an epoxy equivalent of 100 to 4,000.
 17. A composition as claimed in claim 1 wherein said epoxy compounds have an epoxy equivalent of 150 to
 600. 18. A composition as claimed in claim 1 wherein said epoxy compounds are predominantly based on a member selected from the group consisting of bisphenol A, novolak and heterocyclic epoxy compounds.
 19. A composition as claimed in claim 1 further comprising one or more additives selected from the group consisting of catalysts, coupling agents, solvents, wetting aids, foam inhibitors, and plasticizers, said additives being present in a total quantity of up to 30% by weight, based on the total solids content of said composition.
 20. A composition as claimed in claim 1 further comprising a polyaziridine in an amount of 2% to 15% by weight, based on the solids content of said composition.
 21. A composition as claimed in claim 1 further comprising a phenol/resol resin in an amount of 2% to 30% by weight, based on the solids content of said composition.
 22. A composition of matter useful as a film-forming reactive system for the surface-to-surface bonding and/or coating of substrates, said composition comprising an aqueous dispersion comprised of:a polyurethane polymer containing epoxy-reactive functional groups as a first curable resin, said polyurethane polymer having carboxyl groups as epoxy-reactive functional groups, a weight average molecular weight of 10,000 to 30,000, and the sum total of acid value, hydroxyl value and amine value of said polyurethane polymer is on average 0.5 to 5, an acrylate and/or methacrylate homopolymer or copolymer containing carboxyl and/or methylol groups is present in dispersed form as a second curable resin, said acrylate and/or methacrylate homopolymer or copolymer having a weight average molecular weight of 50,000 to 300,000 and a sum total of acid value and OH value of 4 to 10, wherein the ratio by weight of said first curable resin to said second curable resin is in the range from 98:2 to 50:50, an epoxy compound predominantly based on a member selected from the group consisting of bisphenol A, novolak and heterocyclic epoxy compounds, as a curing component for said first curable resin and said second curable resin, said epoxy compound having an epoxy equivalent of 150 to
 600. 23. A process for the production of a substrate coated with a heat-reactivatable adhesive resistant to blocking at room temperature, said process comprising applying a composition as claimed in claim 1 to a substrate and then drying said composition at a maximum temperature of 120° C.
 24. A process as claimed in claim 23 wherein said applying is by roll coating, spray coating, spread coating, knife coating or dip coating.
 25. A process for the production of laminates, said process comprising joining surface-to-surface coated substrates produced by the process claimed in claim 23 to at least one other substrate by reactivation and subsequent curing of the coating at around 140° C. to 170° C.
 26. A process as claimed in claim 25 wherein said laminates are multilayer laminates of metal foils, plastic films, woven cloths, nonwovens, special papers and/or cardboard.
 27. A process as claimed in claim 25 wherein a copper foil is joined to a flexible substrate in the production of a high-temperature-resistant printed circuit.
 28. A process for the production of laminates, said process comprising applying a composition as claimed in claim 1 to at least one of the substrates to be bonded, then immediately joining said substrates surface-to-surface, and curing said composition at about 140° C. to 170° C.
 29. A process as claimed in claim 28 wherein said laminates are multilayer laminates of metal foils, plastic films, woven cloths, nonwovens, special papers and/or cardboard.
 30. A process as claimed in claim 28 wherein a copper foil is joined to a flexible substrate in the production of a high-temperature-resistant printed circuit. 